我有一个模板标签,它最终返回一个“活动”广告列表(检查活动字段的活动是否为True
,然后用查询集从活动中提取广告)
@register.assignment_tag
def get_current_campaigns(amount):
# Get all the campaigns that are active
current_campaigns = Campaign.objects.filter(active=True)
current_campaigns_count = current_campaigns.count()
# To avoid the list index being out of range and throwing an IndexError
# We reduce the amount to match the amount of rows in the model if the
# amount of rows is less than the amount being requested.
if amount > current_campaigns_count:
amount = current_campaigns_count
# Select active campaigns randomly
random_camps = []
for i in range(amount):
random_camps.append(random.choice(current_campaigns))
# prepare all the ads to return
output = []
for campaign in random_camps:
# get all the ads that a campaign has
ads = campaign.advertisement_set.all()
# now select one randomly
ad = random.choice(ads)
# hand it to output
output.append(ad)
# mark that this campaign has been seen
campaign.impressions = F('impressions') + 1
campaign.save()
# checks and sets if the campaign is still active
campaign.check_active()
return output
下面是与之配套的模型:
class Campaign(models.Model):
''' Represents an Advertisement Campaign '''
title = models.CharField(max_length=50, blank=True, verbose_name='Campaign Title')
impressions = models.IntegerField()
impression_limit = models.IntegerField()
created = models.DateTimeField(auto_now_add=True)
active = models.BooleanField(default=False)
def check_active(self):
''' Checks if the Campaign is currently active '''
if self.impressions >= self.impression_limit:
self.active = False
self.save()
奇怪的一点是:每次我访问广告所在的页面,然后在管理中检查它时,对象的印象就会增加2(应该是1),并被标记为False,即使这个if self.impressions >= self.impression_limit
不是真的,它仍然会以某种方式将活动字段更改为False
。你知道吗
你知道为什么会有这种奇怪的行为吗?我可以提供更多的信息,如果需要的话。你知道吗
random.choice
不保证生成非重复项。你知道吗是去这里的路。你知道吗
更新 如果您担心速度,那么this question会解决postgres中的快速随机行选择问题。你知道吗
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